Al-ni-la-si system al-based alloy sputtering target and process for producing the same

ABSTRACT

The present invention relates to an Al—Ni—La—Si system Al-based alloy sputtering target including Ni, La and Si, in which, when a section from (¼)t to (¾)t (t: thickness) in a cross section vertical to a plane of the sputtering target is observed with a scanning electron microscope at a magnification of 2000 times, (1) a total area of an Al—Ni system intermetallic compound having an average particle diameter of 0.3 μm to 3 μm with respect to a total area of the entire Al—Ni system intermetallic compound is 70% or more in terms of an area fraction, the Al—Ni system intermetallic compound being mainly composed of Al and Ni; and (2) a total area of an Al—Ni—La—Si system intermetallic compound having an average particle diameter of 0.2 μm to 2 μm with respect to a total area of the entire Al—Ni—La—Si system intermetallic compound is 70% or more in terms of an area fraction, the Al—Ni—La—Si system intermetallic compound being mainly composed of Al, Ni, La, and Si.

FIELD OF THE INVENTION

The present invention relates to an Al—Ni—La—Si system Al-based alloysputtering target containing Ni, La and Si and a process for producingthe same. In more detail, it relates to an Al—Ni—La—Si system Al-basedalloy sputtering target that may, when a thin film is deposited by theuse of a sputtering target, reduce the number of initial splashesgenerated at an initial stage of sputtering, and a process for producingthe same.

BACKGROUND OF THE INVENTION

An Al-based alloy, being low in the electrical resistivity and easy toprocess, is widely used in a field of flat panel displays (FPDs) such asliquid crystal displays (LCDs), plasma display panels (PDPs),electroluminescent displays (ELDs), field emission displays (FEDs) andMEMS (Micro Electro Mechanical System) displays, touch panels andelectronic papers and is used as materials for interconnection films,electrode films and reflective electrode films.

For instance, an active matrix type liquid crystal display includes athin film transistor (TFT) that is a switching element, a pixelelectrode constituted of a conductive oxide film and a TFT substratehaving an interconnection containing a scanning line and a signal line.As an interconnection material that constitutes the scanning line andsignal line, generally, thin films made of a pure Al or an Al—Nd alloyare used. However, when various kinds of electrode portions formed bythe thin films are directly connected to a pixel electrode, insulatingaluminum oxide is formed at an interface to increase the contactelectrical resistance. Accordingly, so far, a barrier metal layer madeof a refractory metal such as Mo, Cr, Ti or W has been disposed betweenthe Al interconnection material and the pixel electrode to reduce thecontact electrical resistance.

However, in a method of interposing a barrier metal layer such asmentioned above, there is a problem in that a production process becomestroublesome to be high in the production cost.

In this connection, the inventors have proposed, as a technology that,without interposing a barrier metal layer, enables to directly connectan electroconductive oxide film that constitutes a pixel electrode andan interconnection material (direct contact technology), a method inwhich as an interconnection material a thin film of an Al—Ni alloy or anAl—Ni alloy further containing a rare earth element such as Nd or Y isused (see, JP-A-2004-214606). When the Al—Ni alloy is used, at aninterface, electroconductive Ni-containing precipitates are formed tosuppress insulating aluminum oxide is inhibited from generating;accordingly, the contact electrical resistance can be suppressed low.Furthermore, when the Al—Ni-rare earth element alloy is used, the heatresistance can be further improved.

Now, when an Al-based alloy thin film is formed, in general, asputtering process that uses a sputtering target is adopted. Accordingto the sputtering method, plasma discharge is generated between asubstrate and a sputtering target (target material) constituted of amaterial same as that of the thin film, a gas ionized by the plasmadischarge is brought into collision with the target material to knockout atoms of the target material to deposit on the substrate to producea thin film. The sputtering method, different from a vacuum depositionmethod, has an advantage in that a thin film having a composition sameas that of the target material can be formed. In particular, an Al-basedalloy thin film deposited by use of the sputtering method can dissolvean alloy element such as Nd that cannot be dissolved in an equilibriumstate and thereby can exert excellent performance as a thin film;accordingly, the sputtering method is an industrially effective thinfilm producing method and a development of a sputtering target materialthat is a raw material thereof is forwarded.

Recently, in order to cope with the productivity enlargement of FPDs, adepositing rate at the sputtering step tends to be increased more thanever. In order to increase the depositing rate, the sputtering power canbe most conveniently increased. However, when the sputtering power isincreased, sputtering defects such as splashes (fine melt particles) arecaused to generate defects in the interconnection film; accordingly,harmful effects such as deterioration the yield and operationperformance of the FPDs are caused.

In this connection, in order to inhibit the splashes from occurring, forinstance, methods described in JP-A-10-147860, JP-A-10-199830,JP-A-11-293454 and JP-A-2001-279433 have been proposed. Among these, inall of JP-A-10-147860, JP-A-10-199830 and JP-A-11-293454 that are basedon the viewpoint in that the splashes are caused owing to fine voids ina target material texture, a dispersion state of particles of a compoundof Al and a rare earth element in an Al matrix is controlled(JP-A-10-147860), a dispersion state of a compound of Al and atransition metal element in an Al matrix is controlled (JP-A-10-199830)or a dispersion state of an intermetallic compound between an additiveelement and Al in a target is controlled (JP-A-11-293454) to inhibit thesplashes from occurring. Furthermore, JP-A-2001-279433 discloses atechnology in which, in order to reduce the arching (irregulardischarge) that is a cause of the splashes, the hardness of a sputteringsurface is controlled, followed by applying finish working to inhibitsurface defects due to the machining from occurring.

On the other hand, a technology that inhibits a target from warping dueto heating at the production of mainly a large target has been disclosed(JP-A-2006-225687). In JP-A-2006-225687, it is disclosed that, with anAl—Ni-rare earth element alloy sputtering target as an object, when morethan a predetermined number of compounds having an aspect ratio of 2.5or more and a circle equivalent diameter of 0.2 μm or more are presentin a cross section vertical to a target plane, the target can beinhibited from deforming.

As mentioned above, although various technologies for reducing thegeneration of the splashes to reduce the sputtering defects have beenproposed, a further improvement has been demanded. In particular, theinitial splashes occurring in an initial stage of the sputteringdeteriorate the yield of FPDs and thereby cause a serious problem.However, the splash inhibition technologies disclosed in JP-A-10-147860,JP-A-10-199830, JP-A-11-293454 and JP-A-2001-279433 cannot sufficientlyeffectively inhibit the initial splashes from occurring. Furthermore,among Al-based alloys, in an Al-based alloy sputtering target that isuseful as an interconnection material capable of directly connectablewith a elctroconductive oxide film that constitutes a pixel electrodeand is used to form a thin film of an Al—Ni—La—Si system Al-based alloythat is applicable as an interconnection material capable of directlycontactable with a semiconductor layer of a thin film transistor, atechnology that can overcome the above-mentioned problems has not yetbeen proposed.

The inventors have made intensive studies to provide an Al-based alloysputtering target that can reduce the splashes generated during thesputtering deposition, in particular, the initial splashes generated atthe initial stage of the sputtering deposition.

As a result, it was found that both of particle size distributions ofintermetallic compounds (an Al—Ni system intermetallic compound mainlycomposed of Al and Ni and an Al—La system intermetallic compound mainlycomposed of Al and La) contained in an Al—Ni—La system Al-based alloysputtering target have a significant correlation with the generation ofthe initial splashes; accordingly, when the particle size distributionsof the intermetallic compounds are appropriately controlled, an expectedobject can be achieved, and this was previously filed as a patentapplication (Japanese patent application No. 2006-313506). In whatfollows, the above-mentioned invention is called as “precedent Al—Ni—Lasystem Al-based sputtering target” or simply as “the precedentinvention” in some cases.

SUMMARY OF THE INVENTION

The invention was carried out in view of the above-mentionedcircumstances and intends to provide a technology that can reducesplashes, in particular, the initial splashes generated when anAl—Ni—La—Si system Al-based alloy sputtering target containing Ni, Laand Si is used to deposit a film.

After the precedent invention was filed, the inventors have further madeintensive studies on an Al—Ni—La system Al-based alloy sputteringtarget. Specifically, regarding an Al—Ni—La—Si system Al-based alloysputtering target obtained by further adding Si to the Al—Ni—La systemAl-based alloy sputtering target, similarly to the above, intermetalliccompounds contained in the sputtering target were studied in detail.Consequently, it was found that both of particle size distributions ofan intermetallic compound (an Al—Ni system binary intermetallic compoundmainly composed of Al and Ni and an Al—Ni—La—Si system quaternaryintermetallic compound mainly composed of Al, Ni, La and Si) containedin the sputtering target have a significant correlation with thegeneration of the initial splashes; accordingly, when the particle sizedistributions of the intermetallic compounds are appropriatelycontrolled, an expected object can be achieved, whereby the presentinvention have been completed.

Namely, the present invention relates to the following items 1 to 4.

1. An Al—Ni—La—Si system Al-based alloy sputtering target including Ni,La and Si, in which, when a section from (¼)t to (¾)t (t: thickness) ina cross section vertical to a plane of the sputtering target is observedwith a scanning electron microscope at a magnification of 2000 times,

(1) a total area of an Al—Ni system intermetallic compound having anaverage particle diameter of 0.3 μm to 3 μm with respect to a total areaof the entire Al—Ni system intermetallic compound is 70% or more interms of an area fraction, the Al—Ni system intermetallic compound beingmainly composed of Al and Ni; and

(2) a total area of an Al—Ni—La—Si system intermetallic compound havingan average particle diameter of 0.2 μm to 2 μm with respect to a totalarea of the entire Al—Ni—La—Si system intermetallic compound is 70% ormore in terms of an area fraction, the Al—Ni—La—Si system intermetalliccompound being mainly composed of Al, Ni, La, and Si.

2. The Al—Ni—La—Si system Al-based alloy sputtering target according toitem 1, which includes:

Ni in an amount of 0.05 atomic percent to 5 atomic percent;

La in an amount of 0.10 atomic percent to 1 atomic percent; and

Si in an amount of 0.10 atomic percent to 1.5 atomic percent

3. A process for producing the Al—Ni—La—Si system Al-based alloysputtering target according to item 1, the process including:

preparing an Al—Ni—La—Si system Al-based alloy containing Ni in anamount of 0.05 atomic percent to 5 atomic percent, La in an amount of0.10 atomic percent to 1 atomic percent, and Si in an amount of 0.10atomic percent to 1.5 atomic percent;

melting the Al-based alloy at a temperature of 800 to 950° C. to obtaina melt of the Al—Ni—La—Si system Al-based alloy;

gas atomizing the melt of the Al-based alloy at a gas/metal ratio of 6Nm³/kg or more to miniaturize the Al-based alloy;

depositing the miniaturized Al-based alloy on a collector at a spraydistance of 900 to 1200 mm to obtain a preform;

densifying the Al-based alloy preform by means of densifying means toobtain a dense body; and

subjecting the dense body to plastic working.

4. The process according to item 3, in which the Al—Ni—La—Si systemAl-based alloy sputtering target includes:

Ni in an amount of 0.05 atomic percent to 5 atomic percent;

La in an amount of 0.10 atomic percent to 1 atomic percent; and

Si in an amount of 0.10 atomic percent to 1.5 atomic percent.

According to the Al—Ni—La—Si system Al-based alloy sputtering target ofthe invention, as mentioned above, particle size distributions ofintermetallic compounds (an Al—Ni system intermetallic compound mainlycomposed of Al and Ni and an Al—Ni—La—Si system intermetallic compoundmainly composed of Al, Ni, La and Si) present in the sputtering targetare appropriately controlled; accordingly, the splashes, in particular,the initial splashes can be inhibited from generating, whereby thesputtering defects can be effectively suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an SEM reflection electron image in example No. 4 (inventiveexample) of Table 1, FIG. 1B being an image analysis result of an Al—Nisystem intermetallic compound in the SEM reflection electron image, andFIG. 1C being an image analysis result of an Al—Ni—La—Si systemintermetallic compound in the SEM reflection electron image.

FIG. 2A is an SEM reflection electron image of example No. 4 (inventiveexample) of Table 1, FIG. 2B being a diagram showing a result of an EDXanalysis of a composition of 1 (matrix) in FIG. 2A, FIG. 2C being adiagram showing a result of an EDX analysis of a composition of 2 (graycompound) in FIG. 2A, and FIG. 2D being a diagram showing a result of anEDX analysis of a composition of 3 (white compound) in FIG. 2A.

FIG. 3 is a sectional view partially showing an example of an equipmentused to produce a preform.

FIG. 4 is an enlarged diagram of an essential part of X in FIG. 3.

FIG. 5 is a graph showing a particle size distribution of an Al—Nisystem intermetallic compound of example No. 4 (inventive example) ofTable 1.

FIG. 6 is a graph showing a particle size distribution of an Al—Ni—La—Sisystem intermetallic compound of example No. 4 (inventive example) inTable 1.

DESCRIPTION OF THE REFERENCE NUMERALS AND SIGNS

1 induction melting furnace

2 Al-based alloy melt

3 a and 3 b gas atomizer

4 a and 4 b gas hole of bobbin

5 collector

6 nozzle

6 a and 6 b center axis of gas atomizer nozzle

A spray axis

A1 tip of nozzle 6

A2 center of collector 5

A3 point where a horizontal line of a center A2 of a collector 5intersects with a spray axis A

L spray distance

α gas atomizer outlet angle

β collector angle

DETAILED DESCRIPTION OF THE INVENTION

In the specification, an “Al—Ni system intermetallic compound mainlycomposed of Al and Ni” means one in which, when a sputtering target isanalyzed according to a method described below, in which an SEM(Scanning Electron Microscope) provided with an EDX (Energy DispersiveX-ray Fluorescence Spectrometer) is used, peaks of Al and Ni arestrongly detected and peaks of elements other than the above are notsubstantially detected as shown in FIG. 2C. As typical Al—Ni systemintermetallic compounds, a binary intermetallic compound such as Al₃Niis cited.

Furthermore, an “Al—Ni—La—Si system intermetallic compound mainlycomposed of Al, Ni, La and Si” means one in which, when a sputteringtarget is analyzed according to a method similar to the above, peaks ofAl, Ni, La and Si are strongly detected and peaks of elements other thanthe above are not substantially detected as shown in FIG. 2D describedbelow.

Furthermore, in the specification, “the initial splashes can beinhibited from generating (reduced)” means that, when the sputtering iscarried out under the conditions shown in the example described below(sputtering time: 81 sec), an average value of splashes is less than 8spots/cm². Thus, in the invention, the sputtering time is set at 81 secand the splashes at the initial stage of the sputtering deposition areevaluated. That is, the invention is different in the evaluationcriteria from the technologies described in JP-A-10-147860,JP-A-10-199830, JP-A-1 1-293454 and JP-A-2001-279433 in which thegeneration of the initial stage splashes is not evaluated.

Firstly, an Al—Ni—La—Si system Al-based alloy that is an object of theinvention will be described.

An Al-based alloy used in the invention contains Ni, La and Si in Althat is a matrix. The reason why the alloy elements are selected is thatan Al-based alloy film containing the elements is useful not only as aninterconnection material capable of directly connectable with aelctroconductive oxide film that constitutes a pixel electrode but alsoas an interconnection material capable of directly contactable with asemiconductor layer of a thin film transistor. Specifically, when Ni isadded, the interdiffusion of Al and Si in an interface between anAl-based alloy film and a Si semiconductor layer is inhibited fromoccurring. Furthermore, when La in particular in the rare earth elementsis added, the heat resistance is further improved, whereby a hillock(bump-like projection) on a surface of the Al-based alloy film iseffectively inhibited from occurring. Still furthermore, when Si isadded, the interdiffusion of Al and Si in an interface between anAl-based alloy film and a Si semiconductor layer is further effectivelyinhibited from occurring.

Regarding an Al—Ni-rare earth element system Al-based alloy sputteringtarget, JP-A-2006-225687 as well discloses a technology that is targetedto a sputtering target having the above composition. However, differentfrom the present invention, an Al—Ni—La—Si system Al-based alloysputtering target that contains La as a rare earth element is notsubstantially targeted. It goes without saying that, inJP-A-2006-225687, there is no technical idea that, in an Al—Ni—La—Sisystem Al-based alloy sputtering target, in order to inhibit the initialsplash from occurring, particle size distributions of predeterminedintermetallic compounds are controlled. Furthermore, a compound(intermetallic compound) defined in JP-A-2006-225687 is a disc-likecompound having an aspect ratio of 2.5 or more and a circle equivalentdiameter of 0.2 μm or more and is different from the invention having aspherical compound, in terms of the shape of the intermetallic compound.Still furthermore, both are different in production processes as well.As will be detailed below, in the invention, similarly toJP-A-2006-225687, an Al-based alloy preform is preferably produced byuse of a spray forming method. However, in particular, a nozzle diameterφ is controlled to 2.5 to 10 mm and gas pressure is controlled to 0.3 to1.5 MPa to secure a predetermined disc-like compound inJP-A-2006-225687. On the other hand, in the invention, in particular, agas/metal ratio is controlled to 6 Nm³/kg or more to secure a desiredparticle size distribution. In JP-A-2006-225687, the gas/metal ratio isnot utterly taken into consideration; accordingly, even when aproduction process disclosed in JP-A-2006-225687 is adopted, anAl—Ni—La—Si system Al-based alloy sputtering target of the inventioncannot be produced.

Still furthermore, as the splash inhibition technology of an Al-basedalloy sputtering target, for instance, other than JP-A-2006-225687, atechnology in which a dispersion state of a compound or an intermetalliccompound between Al in an Al matrix and a rare earth element iscontrolled is disclosed in JP-A-2004-214606, JP-A-10-147860,JP-A-10-199830 and JP-A-11-293454. However, in all of these, anAl—Ni—La—Si system Al-based alloy sputtering target, that is an objectof the invention is not specifically disclosed. An Al-based alloycontaining La as a rare earth element and Si like the invention is notdisclosed in any of documents disclosed in a section of prior artincluding the above patent documents.

As will be described below, the invention was achieved according to anovel finding that an Al—Ni—La—Si system Al-based alloy sputteringtarget containing La and Si is largely different in a shape of anintermetallic compound from that of an Al—Ni-rare earth element systemAl-based alloy sputtering target that contains a rare earth elementother than La (such as an Al—Ni—Nd system Al-based alloy sputteringtarget disclosed in JP-A-2006-225687). In an Al—Ni—La—Si system Al-basedalloy sputtering target of the invention, as shown in the FIGS. 2A to2D, while a binary intermetallic compound composed of Al and Ni and aquaternary intermetallic compound composed of Al, Ni, La and Si arepresent, a ternary intermetallic compound is not substantially present.On the other hand, in an Al—Ni—Nd system Al-based alloy sputteringtarget disclosed in JP-A-2006-225687, a ternary intermetallic compoundmainly composed of Al, Ni and Nd is present and a binary intermetalliccompound composed of Al and Ni is hardly present. Accordingly, thetechnology in the present invention can be said specialized in anAl—Ni—La—Si system Al-based alloy sputtering target, among theAl—Ni-rare earth element system Al-based alloy sputtering targets.

The content of Ni contained in the Al-based alloy of the invention ispreferably 0.05 atomic percent to 5 atomic percent. The range isdetermined based on experimental results that use the “precedentAl—Ni—La system Al-based alloy sputtering target”. When the lower limitof an amount of Ni is less than 0.05 atomic percent, an area fraction ofan intermetallic compound having a particle diameter of less than 0.3 μmbecomes larger. Accordingly, when a surface of a sputtering targetmaterial is machine-processed, an intermetallic compound falls off toincrease a surface area of irregularities, whereby the number of theinitial splashes increases. On the other hand, when the upper limit ofan amount of Ni exceeds 5 atomic percent, an area fraction of anintermetallic compound having a particle diameter of more than 3 μmincreases. Accordingly, when a surface of a sputtering target materialis machine-processed, irregularities on a surface become larger toincrease in inclusion of non-conductive inclusions such as oxides,resulting in the increase in the number of the initial splashes. Thecontent of Ni is preferably from 0.1 atomic percent to 4 atomic percent,more preferably from 0.2 atomic percent to 3 atomic percent.

Furthermore, the content of La contained in an Al-based alloy of theinvention is preferably from 0.10 atomic percent to 1 atomic percent.The range is determined based on experimental results of the “precedentAl—Ni—La system Al-based alloy sputtering target”. When the lower limitof an amount of La is less than 0.10 atomic percent, an area fraction ofan intermetallic compound having a particle diameter of less than 0.2 μmbecomes larger. Accordingly, when a surface of a sputtering targetmaterial is machine-processed, an intermetallic compound falls off toincrease a surface area of irregularities, whereby the number of theinitial splashes increases. On the other hand, when the upper limit ofan amount of La exceeds 1 atomic percent, an area fraction of anintermetallic compound having a particle diameter of more than 2 μmincreases. Accordingly, when a surface of a sputtering target materialis machine-processed, irregularities of a surface become larger toincrease in inclusion of non-conductive inclusions such as oxides,resulting in the increase in the number of the initial splashes. Acontent of La is preferably from 0.15 atomic percent to 0.8 atomicpercent, more preferably from 0.2 atomic percent to 0.6 atomic percent.

The content of Si contained in an Al-based alloy of the invention ispreferably from 0.10 atomic percent to 1.5 atomic percent. The ranges isdetermined based on experimental results described below. When the lowerlimit of an amount of Si is less than 0.10 atomic percent, an areafraction of an intermetallic compound having a particle diameter of lessthan 0.2 μm becomes larger. Accordingly, when a surface of a sputteringtarget material is machine-processed, an intermetallic compound fallsoff to increase a surface area of irregularities, whereby the number ofthe initial splashes increases. On the other hand, when the upper limitof an amount of Si exceeds 1.5 atomic percent, an area fraction of anintermetallic compound having a particle diameter of more than 2 μmincreases. Accordingly, when a surface of a sputtering target materialis machine-processed, irregularities on a surface become larger toincrease in inclusion of non-conductive inclusions such as oxides,resulting in the increase in the number of the initial splashes. Acontent of Si is more preferably from 0.10 atomic percent to 1.0 atomicpercent.

As shown above, the Al-based alloy used in the invention contains Ni, Laand Si with a remainder being Al and inevitable impurities. As theinevitable impurities, for instance, elements inevitably mingled in aproduction process such as Fe, Cu, C, O and N can be cited.

In the next place, an intermetallic compounds that characterize theinvention will be described.

In a sputtering target of the invention, intermetallic compoundsdescribed below and present in the sputtering target satisfy thefollowing requirements (1) and (2).

(1) Regarding an Al—Ni system intermetallic compound mainly composed ofAl and Ni, a total area of an Al—Ni system intermetallic compound havingan average particle diameter of 0.3 μm to 3 μm with respect to a totalarea of the entire Al—Ni system intermetallic compound is 70% or more interms of the area fraction.

(2) Regarding an Al—Ni—La—Si system intermetallic compound mainlycomposed of Al, Ni, La and Si, a total area of an Al—Ni—La—Si systemintermetallic compound having an average particle diameter from 0.2 μmto 2 μm with respect to a total area of the entire Al—Ni—La—Si systemintermetallic compound is 70% or more in terms of the area fraction.

As mentioned above, in an Al—Ni—La—Si system Al-based alloy sputteringtarget that is an object of the invention, when an intermetalliccompound in an SEM reflection electron image is image analyzed inaccordance with a measurement method that will be detailed below, mainintermetallic compounds that can be observed are only two kinds of abinary intermetallic compound and a quaternary intermetallic compound asmentioned above, and a ternary intermetallic compound observed when anAl—Ni—Nd system Al-based alloy sputtering target that has been typicallyused is observed in accordance with a similar method is notsubstantially present (see FIGS. 2A to 2D).

In the invention, regarding each of the intermetallic compound, based onexperimental results that the initial splashes can be effectivelyinhibited from occurring by increasing an area fraction (occupationratio) of a certain intermetallic compound having a certain averageparticle diameter within a predetermined range, the area fraction of theintermetallic compound is set as large as possible (in the invention,70% or more).

The mechanism of the inhibition of splash generation due to theabove-mentioned intermetallic compounds is assumed as follows.

That is, the reason that the initial splash is generated is generallyconsidered that, when a surface of a sputtering target material ismachine-processed, an intermetallic compound falls off, whereby asurface area of irregularities is increased. Then, (1) regarding anAl—Ni system intermetallic compound mainly composed of Al and Ni, whenan area fraction of an intermetallic compound having an average particlediameter of less than 0.3 μm becomes larger, the generation number ofthe initial splashes increases, and on the other hand when an areafraction of an intermetallic compound having an average particlediameter of more than 3 μm becomes larger, it is considered that owingto an increase in surface irregularities due to machine processing,inclusion of nonconductive inclusions such as oxide increases thereby toresult in an increase in the generation number of the initial splashes.Such a trend is similarly found as well in (2) an Al—Ni—La—Si systemintermetallic compound mainly composed of Al, Ni, La and Si. That is,when an area fraction of an intermetallic compound having an averageparticle diameter of less than 0.2 μm becomes larger, the generationnumber of the initial splashes increases, and on the other hand, when anarea fraction of an intermetallic compound having an average particlediameter of more than 2 μm becomes larger, it is considered that owingto an increase in surface irregularities due to machine processing,inclusion of nonconductive inclusions such as oxide increases thereby toresult in an increase in the generation number of the initial splashes.

Between the Al—Ni system intermetallic compound and the Al—Ni—La—Sisystem intermetallic compound, the range of the average particlediameter that contributes to the inhibition of initial splash generationare a little different from each other. This is assumed because theinterface strengths between the intermetallic compounds and an Al matrixare different. That is, the interface strength between the Al—Ni—La—Sisystem intermetallic compound and an Al matrix is stronger than thatbetween the Al—Ni system intermetallic compound and an Al matrix.

In the invention, the occupation ratio of each intermetallic compoundshaving an average particle diameter satisfying the range is set at 70%or more in terms of area fraction. The larger the occupation ratio isthe better. Regarding each of the intermetallic compounds, theoccupation ratio is preferably 75% or more, more preferably 80% or more.

A measurement method of a particle size distribution of each of theabove-mentioned intermetallic compounds which are objects of theinvention is as follows.

In the beginning, a sputtering target containing Ni, La and Si isprepared.

In the next place, of a measurement plane of the sputtering target(arbitrary three points from a portion from (¼)t (t: thickness) to (¾)tin a cross section in a vertical direction to a plane (rolling planenormal line direction, ND)) is observed by use of an SEM provided withEDX (in an example described below, Quanta 200FEG (trade name, producedby Philips Co., Ltd.) or Supra-35 (trade name, produced by Carl ZeissCo., Ltd.) is used), at a magnification of 2000 times, and a reflectionelectron image is taken. The measurement plane is mirror polished inadvance. One viewing field size is set to substantially 60 μm×50 μm. Aphotographed reflection electron image is image analyzed by use of ananalysis system NanoHunter NS2K-Pro (trade name, produced by NanosystemCorp.), whereby an average particle diameter (circle equivalentdiameter) of each of the Al—Ni system intermetallic compound andAl—Ni—La—Si system intermetallic compound and the area fraction at whicheach of the intermetallic compounds having the average particle diameteroccupies in an entire intermetallic compound are obtained. Thus, thearea fractions in three viewing fields in total are obtained and anaverage value thereof is taken as the area fraction of each of theintermetallic compounds.

According to the measurement method, the Al—Ni system intermetalliccompound and Al—Ni—La—Si system intermetallic compound are readilydifferentiated via color difference (shading difference). A reflectionelectron image of the Al—Ni system intermetallic compound is shown gray.A reflection electron image of the Al—Ni—La—Si system intermetalliccompound is shown white.

For reference purpose, in FIGS. 1A to 1C, regarding example No. 4(inventive example) in Table 1 described in examples described below, anSEM reflection electron image obtained according to the method (FIG.1A), an image of the Al—Ni system intermetallic compound (FIG. 1B) andan image of the Al—Ni—La—Si system intermetallic compound (FIG. 1C) areshown. As shown in FIGS. 1A to 1C, the reflection electron image of theAl—Ni—La—Si system intermetallic compound is shown whiter than that ofthe Al—Ni system intermetallic compound.

Furthermore, in FIGS. 2A to 2D, regarding an SEM reflection electronimage of example No. 4 (inventive example) same as above, compositionsof a matrix (1, in FIG. 2A), a gray compound (2, in FIG. 2A) and a whitecompound (3, in FIG. 2A) are analyzed with EDX and results thereof areshown. It was confirmed that the matrix 1 is, as shown in FIG. 2B,composed only of Al, the gray compound 2 is, as shown in FIG. 2C,composed substantially of Al and Ni and the white compound 3 is, asshown in FIG. 2D, composed substantially of Al, Ni, La and Si.

In the next place, a process for producing a sputtering target of theinvention will be described.

Firstly, an Al—Ni—La—Si system Al-based alloy containing 0.05 atomicpercent to 5 atomic percent of Ni, 0.10 atomic percent to 1 atomicpercent of La and 0.10 atomic percent to 1.5 atomic percent of Si isprepared.

In the next place, using the above-mentioned Al-based alloy, an Al-basedalloy preform (an intermediate body before obtaining a final dense body)is produced preferably according to a spray forming method, followed bydensifying the preform by use of densifying means.

Herein, the spray forming method is a method where various kinds ofmolten metals are atomized with a gas and particles quenched in asemi-molten state/semi-soldification state/solid state are deposited toobtain a preform having a predetermined shape. According to the method,there are various advantages that, in addition that a large preform thatis difficult to obtain according to a melt casting method or a powdermetallurgy method can be obtained in a single process, grains can bemade fine and alloy elements can be uniformly dispersed.

The step for producing a preform includes: melting an Al-based alloy ata temperature substantially in the range of (liquidus temperature +150°C.) to (liquidus temperature +300° C.) to obtain a melt of the Al-basedalloy; gas atomizing the melt of the Al-based alloy under the conditionswith a gas/metal ratio expressed by a ratio of gas outflow/melt outflowof 6 Nm³/kg or more for miniaturization; and depositing the miniaturizedAl-based alloy on a collector under the conditions with a spray distancesubstantially of 900 to 1200 mm to obtain a preform.

In what follows, with reference to FIGS. 3 and 4, the respective stepsfor obtaining a preform will be detailed.

FIG. 3 is a sectional view partially showing an example of an equipmentused to produce a preform of the invention. FIG. 4 is an enlarged viewof as essential part of X in FIG. 3.

An equipment shown in FIG. 3 includes an induction melting furnace 1 formelting an Al-based alloy; gas atomizers 3 a and 3 b disposed below theinduction melting furnace 1; and a collector 5 for depositing a preform.The induction melting furnace 1 includes a nozzle 6 for dropping a melt2 of the Al-based alloy. Furthermore, the gas atomizers 3 a and 3 b,respectively, have gas holes 4 a and 4 b of bobbins for atomizing a gas.The collector 5 includes driving means such as a stepping motor (notshown in the drawing).

In the beginning, an Al-based alloy having above-mentioned compositionis prepared. The Al-based alloy is put in the induction melting furnace1, followed by, preferably in an inert gas (for instance, Ar gas)atmosphere, melting at a temperature substantially in the range of +150°C. to +300° C. to a liquidus temperature of the Al-based alloy.

A melting temperature is generally set to a temperature in the range of(liquidus temperature +50° C.) to (liquidus temperature +200° C.) (see,for example, JP-A-09-248665). However, in the invention, in order toappropriately control the particle size distributions of the two kindsof intermetallic compounds, the above-mentioned range is set. In thecase of the Al—Ni—La—Si system Al-based alloy that is an object of theinvention, the melting temperature is set substantially in the range of800 to 950° C. When the melting temperature is less than 800° C., anozzle is clogged in the spray forming. On the other hand, when themelting temperature exceeds 950° C., since a liquid drop temperaturebecomes higher and whereby an area fraction at which an Al—Ni systemintermetallic compound having an average particle diameter of 3 μm ormore occupies increases, desired splash inhibition effect cannot beobtained (refer to examples described below). The melting temperature ofan alloy is preferably in the range of (liquidus temperature +150° C.)to (liquidus temperature +300° C.). In the case of the Al—Ni—La—Sisystem Al-based alloy that is an object of the invention, the meltingtemperature is preferably in the range of 800 to 950° C., morepreferably in the range of 850 to 950° C.

In the next place, the alloy melt 2 of obtained as mentioned above isdropped into a chamber (not shown in the drawing) having an inert gasatmosphere through a nozzle 6. In the chamber, from gas holes 4 a and 4b of bobbins provided to gas atomizers 3 a and 3 b, a jet flow of apressurized inert gas is sprayed to the alloy melt 2 thereby tominiaturize the alloy melt.

The gas atomization is preferably carried out, as mentioned above, withan inert gas or a nitrogen gas, and whereby the melt can be inhibitedfrom oxidizing. As the inert gas, for instance, an argon gas can becited.

Herein, the gas/metal ratio is set at 6 Nm³/kg or more. The gas/metalratio is expressed by a ratio of gas outflow (Nm³)/melt outflow (kg). Inthe specification, the gas outflow means a sum total (finally usedamount) of a gas flowed out of the gas holes 4 a and 4 b of the bobbinsfor gas atomizing the melt of the Al-based alloy. Furthermore, in thespecification, the melt outflow means a sum total of a melt flowed outof a melt outflow port (nozzle 6) of a vessel (induction melt furnace 1)in which the melt of the Al-based alloy is present.

When the gas/metal ratio is less than 6 Nm³/kg, a size of a liquid droptends to be larger to thereby lower a cooling rate. Accordingly, anoccupation ratio of the Al—Ni system intermetallic compound having anaverage particle diameter of more than 3 μm increased to thereby resultin incapability of obtaining a desired effect (refer to examplesdescribed below).

The larger the gas/metal ratio the better. For instance, the gas/metalratio is preferably 6.5 Nm³/kg or more, more preferably 7 Nm³/kg ormore. The upper limit thereof is not particularly restricted. However,from the viewpoints of the stability of liquid drop flow during the gasatomizing and the cost, the upper limit of the gas/metal ratio ispreferably set at 15 Nm³/kg, more preferably set at 10 Nm³/kg.

Furthermore, when an angle that center axes 6 a and 6 b of the opposinggas atomizing nozzles form is expressed by 2α, α is preferablycontrolled in the range of 1 to 10°. An angle 2α that center axes 6 aand 6 b of the opposing gas atomizing nozzles form means, as shown inFIG. 4, a total angle of the respective inclinations α of the gasatomizers 4 a and 4 b relative to a line (corresponding to a spray axisA) when the melt 2 vertically drops. In what follows, the α is called asa “gas atomizer outlet angle α”. The gas atomizer outlet angle α ispreferably in the range of 1° to 7°.

Subsequently, thus miniaturized Al-based alloy (liquid drops) isdeposited on the collector 5 to obtain a preform.

Herein, a spray distance is preferably controlled in the range of 900 to1200 mm. The spray distance defines a deposition position of a liquiddrop and, as shown in FIG. 3, it means a distance L from a tip end ofthe nozzle 6 (A1 in FIG. 3) to a center of the collector 5 (A2 in FIG.3). As will be described below, since the collector 5 tilts at acollector angle β, the spray distance L means, strictly speaking, adistance between the tip end of the nozzle 6 and a point (A3 in FIG. 3)in which a horizontal line of the center A2 of the collector 5intersects with a spray axis A. Herein, the spray axis A defines, forthe sake of convenience of description, a direction along which a liquiddrop of the Al-based alloy falls straight.

In general, the spray distance in the spray forming is controlled atsubstantially 500 mm. However, in the invention, in order to obtaindesired particle size distributions of the two kinds of intermetalliccompounds, the above-mentioned range is adopted (refer to examplesdescribed below). When the spray distance is less than 900 mm, liquiddrops in a high temperature state are deposited on the collector to makethe cooling rate slower. Accordingly, an occupation ratio of an Al—Nisystem intermetallic compound having an average particle diameter of 3μm or more increases to thereby result in incapability of obtaining adesired effect. On the other hand, when the spray distance exceeds 1200mm, the yield is deteriorated. The spray distance is preferablysubstantially in the range of 950 to 1100 mm.

Furthermore, the collector angle β is preferably controlled in the rangeof 20 to 45°. The collector angle β means, as shown in FIG. 3, aninclination of the collector 5 to the spray axis A.

In the above, a preferable method for obtaining the preform wasdescribed.

According to a standard method that thus obtained preform of Al-basedalloy is densified by use of densifying means to obtain a dense body,followed by applying plastic working to the dense body, a sputteringtarget can be produced.

In the beginning, by applying the densifying means to the preform, anAl-based alloy dense body is obtained. As the densifying means, a methodof pressurizing a preform in a substantially equal pressure direction,in particular, a hot isostatic pressing (HIP) where pressure is appliedunder heating, is preferably applied. Specifically, HIP treatment isapplied preferably, for instance, under pressure of 80 MPa or more andat a temperature in the range of 400 to 600° C. The period for HIPtreatment is preferably substantially in the range of 1 to 10 hours.

Then, the Al-based alloy dense body is forged to obtain a slab.

The forging condition is not particularly restricted so long as a methodthat is usually used to produce a sputtering target is used. However,the forging is preferably applied after an Al-based alloy dense bodybefore forging is heated at a temperature of substantially 500° C. forsubstantially 1 to 3 hours.

To the slab thus obtained as mentioned above, a rolling process isapplied under the conditions of a rolling temperature of 300 to 550° C.and a total rolling reduction of 40 to 90%. As will be shown in examplesdescribed below, in the invention, the rolling conditions have to becontrolled delicately as mentioned above. When the rolling is appliedunder conditions where any one of the conditions is outside of therange, desired crystallographic orientations cannot be obtained.

Herein, the total rolling reduction is expressed by the followingformula.

Total rolling reduction (%)={(thickness before rolling)−(thickness afterrolling)}/(thickness before rolling)×100

The Al-based alloy produced by the spray forming method, being difficultto cause a change in a structure during the processing, can be producedaccording to either one of the cold rolling and hot rolling. However, inorder to heighten the processing rate per one pass, an Al-based alloymaterial can be effectively heated and processed in a temperature rangelow in the deformation resistance; accordingly, the hot rolling ispreferably adopted.

In the next place, a heating process (heat treatment or annealing) isapplied at a temperature in the range of 250 to 500° C. for 0.5 to 4hours. An atmosphere during the heating process, without particularlyrestricting, can be any one of air, inert gas and vacuum. However, inviewpoint of the productivity and cost, heating in air is preferred.

When a machining process is applied into a predetermined shape after theheat treatment, a desired sputtering target can be obtained.

The Al—Ni—La—Si alloy target according to the invention is particularlypreferably used when an interconnection material of an Al—Ni—La—Si alloyfilm capable of directly connectable with a elctroconductive oxide filmthat constitutes a pixel electrode and an interconnection material of anAl—Ni—La—Si alloy film capable of directly contactable with asemiconductor layer of a thin film transistor are produced.

EXAMPLES

Hereinafter, with reference to examples, the invention will be morespecifically described. However, the invention is not restricted to orby the examples below, and can be carried out by appropriately modifyingwithin a range that can adapt to the gist of the invention and all theseare contained in the technical range of the invention.

Example 1

With Al-based alloys having various compositions shown in tables 1 and2, according to the following spray forming method, Al-based alloypreforms (density: substantially 50 to 60%) were obtained.

(Spray Forming Conditions)

Melting temperature: 950° C.

Gas/metal ratio: 7 Nm³/kg

Spray distance: 1000 mm

Gas atomizer outlet angle (α): 7°

Collector angle (β): 35°

Thus obtained preform was sealed in a capsule, followed by deaerating,further followed by applying the hot isostatic pressing (HIP) to anentirety of the capsule, whereby an Al—Ni—La—Si system Al-based alloydense body was obtained. The HIP process was carried out at a HIPtemperature of 550° C., under HIP pressure of 85 MPa for the HIP time of2 hours.

Thus obtained dense body was forged into a slab metal material, followedby rolling so that a plate thickness may be substantially same as thatof a final product (target), further followed by annealing and machining(corner cutting work and turning work), whereby a disc-shaped Al—(0.02to 5.5 atomic percent Ni)—(0.05 to 1.5 atomic percent La)—(0.05 to 2atomic percent) Si system Al-based alloy sputtering target (size:diameter 101.6 mm×thickness 5.0 mm) was produced. Detailed conditionsare as follows.

Heating conditions before forging: 500° C. for 2 hours

Heating conditions before rolling: 400° C. for 2 hours

Total rolling reduction: 50%

Annealing conditions: 400° C. for 1 hour

In the next place, with each of the sputtering targets obtainedaccording to the above-mentioned method, the number of splashes (initialsplash) occurring when the sputtering is carried out under the followingconditions was measured.

Firstly, to a Si wafer substrate (size: diameter 100.0 mm×thickness 0.50mm), DC magnetron sputtering was carried out by use of a sputteringequipment, “Sputtering System HSM-542S” (trade name, produced byShimadzu Corp.). The sputtering conditions were as follows.

Back pressure: 3.0×10⁻⁶ Torr or less, Ar gas pressure: 2.25×10⁻³ Torr,

Ar gas flow rate: 30 sccm, sputtering power: 811 W,

distance between a substrate and a sputtering target: 51.6 mm, substratetemperature: room temperature

sputtering time: 81 sec

Thus, with regard to one sputtering target, 16 thin films were formed.

In the next place, by use of a particle counter (trade name: WaferSurface Detector WM-3, produced by Topcon Corp.), positionalcoordinates, sizes (average particle diameter) and number of particlesfound on a surface of the thin film were measured. Here, one of whichsize is 3 μm or more is regarded as a particle. Thereafter, the thinfilm surface was observed with an optical microscope (magnification:1000 times) and, with one of which shape is semispherical regarded assplash, the number of splashes per unit area was measured.

In detail, a step of carrying out the sputtering of one thin film wascontinuously repeated 16 times similarly with a Si wafer substrateexchanging each time, and an average value of the numbers of thesplashes was taken as “occurrence frequency of initial splashes”. In thepresent example, one of which occurrence frequency of initial splashesis less than 8 spots/cm² is taken as “effective in reducing the initialsplashes: acceptable (A)” and one of which occurrence frequency ofinitial splashes is 8 spots/cm² or more was taken as “ineffective inreducing the initial splashes: unacceptable (B)”.

The results thereof are shown together in tables 1 and 2. For thepurpose of reference, regarding example No. 4 (inventive example) ofTable 1, a particle size distribution of an Al—Ni system intermetalliccompound is shown in FIG. 5 and a particle size distribution of anAl—Ni—La—Si system intermetallic compound is shown in FIG. 6. In FIG. 6,for convenience sake, only a particle size distribution up to 1.2 μm inparticle size is shown. However, particles having a size exceeding 1.2μm in particle size were not at all found.

TABLE 1 Area fraction of intermetallic compound (%) Al—Ni—La—Si Al—Nisystem system Ni La Si intermetallic intermetallic Initial splashcontent content content Melting Gas/metal Spray compound compoundOccurrence (atomic (atomic (atomic temperature ratio distance having asize having a size of frequency No. percent) percent) percent) (° C.)(Nm³/kg) (mm) of 0.3 to 3 μm 0.2 to 2 μm (number/cm²) Judgement 1 2 0.350.05 950 7 1000 88.2 67.2 14 B 2 2 0.35 0.10 950 7 1000 90.5 85.3 6 A 32 0.35 0.50 950 7 1000 90.2 88.9 5 A 4 2 0.35 1.00 950 7 1000 90.0 96.56 A 5 2 0.35 1.50 950 7 1000 89.3 91.1 7 A 6 2 0.35 2.00 950 7 1000 88.668.4 24 B

From table 1, considerations can be made as follows.

In example Nos. 2 to 5, particle size distributions of the Al—Ni systemintermetallic compound and Al—Ni—La—Si system intermetallic compound areappropriately controlled. Accordingly, the initial splash reductioneffect is excellent.

On the other hand, example No. 1 is an example where an Al-based alloycontaining less Si was used, and example No. 6 is an example where anAl-based alloy much in the content of Si was used. In each thereof,since the total area fraction of the Al—Ni—La—Si system intermetalliccompound that contributes to the inhibition of splash generation wasslight, the above-mentioned examples could not effectively inhibit thesplash from occurring.

TABLE 2 Area fraction of intermetallic compound (%) Al—Ni—La—Si Al—Nisystem system intermetallic intermetallic Initial splash Ni content Lacontent Si content Melting Gas/metal Spray compound compound Occurrence(atomic (atomic (atomic temperature ratio distance having a size havinga size frequency No. percent) percent) percent) (° C.) (Nm³/kg) (mm) of0.3 to 3 μm of 0.2 to 2 μm (number/cm²) Judgement  7 0.02 0.35 1.00 9507 1000 66.5 65.7 30 B  8 0.05 0.35 1.00 950 7 1000 86.4 83.1 6 A  9 20.35 1.00 950 7 1000 90.0 96.5 6 A (Same as No. 4 in table 1) 10 5 0.351.00 950 7 1000 84.0 79.7 7 A 11 5.5 0.35 1.00 950 7 1000 68.3 67.8 27 B12 2 0.05 1.00 950 7 1000 92.5 64.3 13 B 13 2 0.1 1.00 950 7 1000 94.187.2 5 A 14 2 0.35 1.00 950 7 1000 90.0 96.5 6 A (Same as No. 4 intable 1) 15 2 1 1.00 950 7 1000 96.0 77.7 6 A 16 2 1.5 1.00 950 7 100092.2 63.1 16 B

From table 2, considerations can be made as follows.

In example Nos. 8 to 10 and 13 to 15, particle size distributions of theAl—Ni system intermetallic compound and Al—Ni—La—Si system intermetalliccompound are appropriately controlled. Accordingly, the initial splashreduction effect is excellent.

On the other hand, example No. 7 is an example where an Al-based alloycontaining less Ni was used, and example No. 11 is an example where anAl-based alloy much in the content of Ni was used. In each thereof,since the total area fraction of the Al—Ni system intermetallic compoundand the Al—Ni—La—Si system intermetallic compound that contributes tothe inhibition of splash generation was slight, the above-mentionedexamples could not effectively inhibit the splash from occurring.

Additionally, No. 12 is an example where an Al-based alloy containingless La was used, and example No. 16 is an example where an Al-basedalloy much in the content of La was used. In each thereof, since thetotal area fraction of the Al—Ni—La—Si system intermetallic compoundthat contributes to the inhibition of splash generation was slight, theabove-mentioned examples could not effectively inhibit the splash fromoccurring.

The invention was detailed with reference specified embodiments.However, it is obvious to a person skilled in the art that the inventionmay be variously modified and corrected without deviating from thespirit of the invention.

This application is based on Japanese Patent Application No. 2007-192214filed on Jul. 24, 2007 and an entirety thereof is incorporated herein byreference.

Furthermore, all references cited here are incorporated by reference.

1. An Al—Ni—La—Si system Al-based alloy sputtering target comprising Ni,La and Si, wherein, when a section from (¼)t to (¾)t (t: thickness) in across section vertical to a plane of the sputtering target is observedwith a scanning electron microscope at a magnification of 2000 times,(1) a total area of an Al—Ni system intermetallic compound having anaverage particle diameter of 0.3 μm to 3 μm with respect to a total areaof the entire Al—Ni system intermetallic compound is 70% or more interms of an area fraction, the Al—Ni system intermetallic compound beingmainly composed of Al and Ni; and (2) a total area of an Al—Ni—La—Sisystem intermetallic compound having an average particle diameter of 0.2μm to 2 μm with respect to a total area of the entire Al—Ni—La—Si systemintermetallic compound is 70% or more in terms of an area fraction, theAl—Ni—La—Si system intermetallic compound being mainly composed of Al,Ni, La, and Si.
 2. The Al—Ni—La—Si system Al-based alloy sputteringtarget according to claim 1, which comprises: Ni in an amount of 0.05atomic percent to 5 atomic percent; La in an amount of 0.10 atomicpercent to 1 atomic percent; and Si in an amount of 0.10 atomic percentto 1.5 atomic percent.
 3. A process for producing the Al—Ni—La—Si systemAl-based alloy sputtering target according to claim 1, said processcomprising: preparing an Al—Ni—La—Si system Al-based alloy containing Niin an amount of 0.05 atomic percent to 5 atomic percent, La in an amountof 0.10 atomic percent to 1 atomic percent, and Si in an amount of 0.10atomic percent to 1.5 atomic percent; melting said Al-based alloy at atemperature of 800 to 950° C. to obtain a melt of the Al—Ni—La—Si systemAl-based alloy; gas atomizing the melt of said Al-based alloy at agas/metal ratio of 6 Nm³/kg or more to miniaturize said Al-based alloy;depositing said miniaturized Al-based alloy on a collector at a spraydistance of 900 to 1200 mm to obtain a preform; densifying said Al-basedalloy preform by means of densifying means to obtain a dense body; andsubjecting the dense body to plastic working.
 4. The process accordingto claim 3, wherein the Al—Ni—La—Si system Al-based alloy sputteringtarget comprises: Ni in an amount of 0.05 atomic percent to 5 atomicpercent; La in an amount of 0.10 atomic percent to 1 atomic percent; andSi in an amount of 0.10 atomic percent to 1.5 atomic percent.